Pasteurized in-shell chicken eggs

ABSTRACT

A method of pasteurizing in-shell chicken eggs by heating eggs until a central portion of the yolks of the eggs is at a temperature between 128° F. to 138.5° F. That temperature is maintained and controlled for times within parameter line A and parameter line B of FIG. 1 and sufficient that any Salmonella species present in the yolk is reduced by at least 5 logs but insufficient that an albumen functionality of the egg measured in Haugh units is substantially less than the albumen functionality of a corresponding unpasteurized in-shell egg.

This application is a divisional of Ser. No. 08/962,766, now U.S. Pat.No. 5,843,505 filed on Nov. 3, 1997, which application is in turn acontinuation of Ser. No. 08/519,184, filed Aug. 25, 1995, now abandoned.

The present invention relates to pasteurized in-shell chicken eggs andto a method for production thereof, and, more particularly, to such eggsand method where certain pathogens whenever present in the eggs arereduced in quantity to a level safe for human consumption while at thesame time the functionality of the eggs is preserved, particularly thealbumen functionality, such that the pasteurized eggs are substitutablefor fresh, unpasteurized eggs in most consumption uses.

BACKGROUND OF THE INVENTION

The term pasteurization is used herein in connection with the presentinvention in the general sense that the term is applied to other foodproducts, e.g. pasteurized milk, in that the present pasteurized eggsare partially sterilized at temperatures which destroy objectionablemicroorganisms, without major changes in the functionality of the eggs.In this regard, food products are conventionally heated at temperaturesand for times so as to sufficiently destroy pathogenic microorganisms,which may be contained in the food, so that the pasteurized food is safefor human consumption. In order to provide a pasteurized food safe forhuman consumption, it is not necessary that all pathogenicmicroorganisms in the food be destroyed, but it is necessary that thosepathogenic microorganisms be reduced to such a low level that theorganisms cannot produce illness in humans of usual health andcondition. For example, fresh whole milk may contain virulent pathogenicmicroorganisms, most notably microorganisms which cause tuberculosis inhumans, and during pasteurization of the milk, those pathogenicmicroorganisms are reduced to such low levels that the milk is safe forconsumption by humans of ordinary health and condition. In the case ofsome microorganisms, however, usual pasteurization temperatures andtimes can completely destroy those microorganisms. Milk so pasteurizeddoes not have major changes in the functionality thereof. The taste andtexture of pasteurized milk is slightly changed, but those changes arenot of practical significance to most consumers thereof.

Heat destruction of microorganisms in eggs has long been known in thatthe eggs were cooked sufficiently to effect destruction thereof. Forexample, when frying an egg, fried to a reasonable hardness,microorganism destruction will occur. Likewise, when boiling an egg to ahard-boiled state, heat destruction of microorganisms in the egg willoccur. However, with these cooking processes, major changes in thefunctionality of the egg occurs, e.g. coagulation of the yolk and white,and, thus, this is not pasteurization in the usual sense, as explainedabove.

Recently, pasteurization of liquid chicken eggs (eggs out of the shell)has been commercially practiced. The process, very basically, involvesheating liquid chicken eggs for short times at higher temperatures toreduce any pathogenic microorganisms therein such that the pasteurizedliquid chicken eggs are safe for human consumption, while, at the sametime, major changes in functionality do not occur. See, for example,U.S. Pat. No. 4,808,425.

However, the art has long since struggled with pasteurizing in-shellchicken eggs. While in-shell eggs may be heated sufficiently to destroymicroorganisms, the art has not, at the same time, been able tosubstantially retain the functionality of the eggs. The functionality isdetermined by various tests, but a more basic test is that of thealbumen functionality, which test measures the whipped volume, understandard conditions, of whipped liquid albumen, as measured in Haughunits.

In the case of liquid chicken eggs (not in the shell), by carefulcontrol of the time and temperature of heating the liquid eggs, usuallywith a short time, high temperature (HTST) apparatus, pasteurization canbe achieved while retaining, at least substantially, the functionalityof the eggs. This is particularly true when the liquid eggs are heatedfor pasteurization purposes in a very thin film, where the temperatureand time of heating of the liquid eggs can be very carefully controlled.

In liquid eggs, the yolk may or may not be mixed with the albumen. Ascan be appreciated, however, with in-shell chicken eggs (also referredto as "shell eggs"), not only is the mass of the egg substantiallydifferent from the mass of a unit of thin film of liquid eggs, but theyolk is essentially centrally positioned in the shell. Accordingly,while the art has struggled for some time to carefully controltemperatures and times for pasteurizing in-shell eggs, none of thoseefforts in the art have been successful in terms of both reducingpathogenic microorganisms found in chicken eggs to a level safe forhuman consumption while maintaining essentially the same functionalityof the eggs as unpasteurized eggs. As a result, no commercial processfor pasteurizing in-shell eggs and no commercial pasteurized in-shelleggs have been available.

The art has taken many different approaches in attempts to pasteurizein-shell eggs. See, for example, U.S. Pat. Nos. 1,163,873; 2,423,233;2,673,160; and 3,658,558. The more prevalent approaches involve heatingthe in-shell eggs, usually in a water bath, for various times and atvarious temperatures, as specified by the various investigators in theart. These times and temperatures specified by the various investigatorsvary widely, and this is because all of those approaches involve acompromise either in the degree of safety achieved or in the quality ofthe functionality retained.

In this latter regard, if the in-shell egg is heated in a water bath,where the water bath temperature and time of heating are specified bythe investigator, one of two results have generally occurred. The firstresult is that, when higher temperatures and longer times are specified,while the egg may be acceptably reduced in microorganism content, thefunctionality of the egg is also considerably reduced, such that the eggis no longer substitutable for unpasteurized eggs in either usual homecooking, e.g. frying, or in conventional baking recipes. The otherresult, when using lower temperatures of the water bath and shortertimes, while the functionality of the egg is substantially maintained,the decrease in pathogenic microorganisms, which may be present in theeggs, is severely compromised, and the egg may be safer but not be safefor human consumption. While eggs processed according to this latterapproach can be said to be safer to eat, in that there is some reductionof pathogenic microorganisms in the eggs, the eggs are not pasteurizedin the sense as set forth above, i.e. that they are safe for consumptionby humans of ordinary health and condition.

Faced with the above difficulties, that art searched for intermediatewater bath temperatures and dwell times where functionality of the eggis preserved and microorganisms are substantially reduced.Unfortunately, these searches have generally resulted in the worst ofboth of the results noted above, i.e. both reduced functionality of theegg and still insufficient reduction in microorganisms, which result isless desirable than either of the two above-noted general results.

Accordingly, therefore, the art has been on the horns of a dilemma, i.e.if the times of dwell and temperatures of the water bath are high enoughto substantially reduce the microorganism content of in-shell eggs, thenthe functionality of the eggs is substantially reduced, while if thetimes of dwell and temperatures of the water bath are sufficiently lowas to substantially maintain the functionality of the eggs, the eggs arenot sufficiently reduced in microorganism content so as to bepasteurized.

Pathogenic microorganisms are introduced into chicken eggs by twoprincipal routes. Firstly, pathogens are introduced into the in-shelleggs from environmental contamination. This environmental contaminationmay occur through a variety of causes, but typically, infected chickensor mice in commercial egg-laying chicken houses deposit feces whichcontact the shell of a laid egg. Certain microorganisms, especiallySalmonella, when in contact with the shell of the egg, can penetratethat shell, especially through small fissures or pores in the shell.That contamination is, therefore, from the outside of the shell into theegg, and the contamination remains, largely, in the albumen near theshell. This contamination can be very substantially reduced by theabove-noted approaches of the prior art, since, when the egg is placedin a water bath heated to the temperatures suggested by the art, this issufficient to heat the albumen near the shell and substantially destroypathogens which may have penetrated the shell from environmentalcontamination. In this sense, the egg is, indeed, safer to eat.

The second route of contamination in the eggs is systemic, and thisposes a far more difficult problem. Typically, feces of infectedchickens or mice are ingested by the chicken during feeding, and thatinfection becomes systemic in the chicken. Certain organisms, verynotably Salmonella enteritidis, enter the bloodstream of the chicken andpass, trans-ovarially, into the interior of the egg itself. Mostespecially, that systemic contamination occurs in the yolk of the egg,although that contamination can also easily extend into the albumen. Inthis type of contamination, the prior art approaches, as noted above,are ineffective toward substantially reducing microorganisms in theeggs, including the yolk, while at the same time maintaining thefunctionality of the eggs.

While many suggestions have been made in the prior art, principally, awater bath is heated to specified temperatures (although air, oil andthe like heat transfer media have been suggested), and the in-shell eggsare then placed in that heated water bath and dwell therein for aspecified length of time. It is generally assumed that the yolktemperature will come to equilibrium with the water bath temperatureafter a sufficiently long dwell time of the eggs.

Unfortunately, specifying the temperature of the water bath and the timeof dwell of the eggs therein does not necessarily specify temperatureswithin the eggs, and especially the yolks. This is because eggs can varyin one or more of weight, size, shape, composition (e.g. relative sizeof yolk and air sack) and density, all of which affects the heattransfer properties of a particular egg in the water bath at thespecified temperatures. Thus, when operating in water baths at specifiedtemperatures within specified time ranges, the temperature within aparticular egg, and especially the yolk, is entirely problematic, and,hence, the control of the prior art approaches toward pasteurizing eggs,especially in regard to yolk contamination, has been completelyinadequate and more or less is a matter of chance--see, for example, WO95/14388.

The specified temperatures of the water baths in the prior art varyconsiderably, with some investigators taking the approach of relativelylow temperature baths, e.g. as low as about 100° F., with long dwellperiods of the eggs, while other investigators took the approach of hightemperature baths, e.g. up to 160° F., with relatively short dwellperiods of the eggs, and others took an intermediate approach, e.g. 130°F. to 140° F., with intermediate dwell periods, e.g. 50 minutes.However, no matter which of these approaches is adopted, as explainedabove, the art simply has not found combinations of temperatures ofwater baths and times of dwell which will ensure eggs safe for humanconsumption, i.e. pasteurized eggs, including pasteurization of theyolks, while at the same time maintaining the functionality of the eggs.Accordingly, it would be a very substantial benefit to the art toprovide a method for pasteurizing eggs where the eggs are not onlypasteurized, i.e. safe for consumption by humans of ordinary health andcondition, but which also assures that the functionality of the eggs issubstantially retained.

BRIEF SUMMARY OF THE INVENTION

Very briefly, the present invention provides pasteurization of anin-shell chicken egg, i.e. safe to eat by humans of ordinary health andcondition, by achieving a 5 log reduction of Salmonella species whichmay be present in the egg by controlling the yolk temperature withinrelatively narrow limits so that both the pasteurization is achieved andthe functionality of the egg is not substantially decreased. In theseregards, the present invention is based on several primary discoveriesand several subsidiary discoveries.

As a primary discovery, it was found that, if the temperature and dwelltime of the yolk is at a certain correlation of temperature and time orwithin a 95% confidence level deviation, Salmonella species which may bepresent in the egg yolk, as well as the albumen, can be reduced by atleast 5 logs, which reduction is sufficient for true pasteurization,i.e. safe for consumption by humans of ordinary health and condition,while at the same time there is a retention of functionality of theeggs.

As a subsidiary discovery in this regard, it was found that, ifSalmonella species are reduced by that at least 5 logs, othermicroorganisms found in the egg are also reduced, such that the egg ispasteurized in respect to those other microorganisms.

As a second primary discovery, it was found that, if the egg ispasteurized according to that certain correlation, or within the limitsof deviations noted above, the albumen functionality of the egg,measured in Haugh units, is not substantially deteriorated, as comparedwith a corresponding unpasteurized in-shell egg.

As a third primary discovery, it was found that, in order to effectivelypasteurize an egg, the yolk temperature of that egg must be controlledwithin relatively narrow temperature limits.

As a subsidiary discovery in this regard, it was found that thetemperature of the yolk must be controlled in a range of from 128° F. to138.5° F. At temperatures of the yolk below 128° F., adequatepasteurization will not occur. On the other hand, at temperatures of theyolk above 138.5° F., the functionality of the egg substantiallydecreases.

As a fourth primary discovery, it was found that, within this range ofyolk temperatures, the dwell time of the yolk at a selected temperaturemust be relatively closely correlated to that temperature. If the dwelltime is significantly below that correlation, pasteurization will notoccur. On the other hand, if the dwell time is significantly above thatcorrelation, then the functionality of the egg is substantiallydeteriorated.

As a subsidiary discovery in this regard, it was found that the limitsof deviation from that correlation which are permissible to achieve bothpasteurization and retention of functionality are relatively small.Deviations should be no greater than that which will provide a 95%statistical confidence level of pasteurization. Thus, the limits ofdeviation from that specific correlation must be carefully observed.

Thus, broadly stated, the present invention provides a method ofpasteurizing an in-shell chicken egg comprising heating the egg until acentral portion of the yolk of the egg is controlled within the range of128° F. to 138.5° F., and maintaining that controlled yolk temperaturefor times within parameter line A and parameter line B of FIG. 1 annexedhereto and sufficient that a Salmonella species that may be present inthe egg is reduced in amount by at least 5 logs but insufficient that analbumen functionality of the egg measured in Haugh units issubstantially less than the albumen functionality of a correspondingunpasteurized in-shell egg.

The invention also provides a pasteurized in-shell chicken eggcomprising a pasteurized central portion of a yolk of the egg having atleast a 5 log reduction of a Salmonella species that may be present inthe yolk in its unpasteurized form. The so-pasteurized egg will have analbumen functionality measured in Haugh units not substantially lessthat the albumen functionality of a corresponding unpasteurized in-shellegg.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a graph showing the required correlation between thetemperatures of a central portion of the yolk of an egg during thepasteurization process and the log (base 10) of time at which thatcentral portion of the yolk of the egg dwells at such temperatures. Thatgraph also shows permissible limits of deviation from that correlation,indicated by parameter lines A and B.

DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention is directed to in-shell chicken eggs, and itcannot be extrapolated to other in-shell poultry eggs. In-shell poultryeggs from different birds vary considerably in the mass, propensity forcoagulation of the albumen and yolk, temperatures and dwell times foradequate pasteurization, heat transfer properties, and usualfunctionalities. For example, it has been found that an in-shell duckegg, which is probably the closest poultry egg to a chicken egg, cannotbe pasteurized to a 5 log cycle reduction of a Salmonella species foundin chicken eggs and maintain functionality with the method of thepresent invention. In attempts to pasteurize in-shell duck eggs by thismethod, it was found that the time and temperature correlations foundfor in-shell chicken eggs were inappropriate for in-shell duck eggs.Therefore, it is emphasized that the invention relates only to in-shellchicken eggs, and the method of the invention cannot be consideredworkable to any other in-shell poultry egg. See Dutch Patent No. 72,454.

As opposed to the prior art, briefly summarized above, which relied uponthe temperature of the medium for heating the egg, e.g. usually water,the present invention relies upon the temperatures of the yolk of theegg, along with the correlated dwell times of the yolk at thosetemperatures, and for this reason, the particular medium in which theegg is heated is not critical, as opposed to that of the prior art.Thus, in the prior art, since, generally speaking, the temperature ofthe heating medium was controlled and the temperature of the yolk wasessentially uncontrolled, the choice of heating medium was a criticalchoice because the heat transfer properties of a particular mediumgreatly influenced the results of the process. For that reason, most ofthe approaches in the prior art chose water as the heating medium, sincethe temperature of the water in a heating bath could be carefullycontrolled, and heat transfer from the water bath to the egg isaccelerated. The present invention does not rely on controlling thetemperature of the heating medium to effect pasteurization. Conversely,the present invention relies on controlling the temperature of the yolk.Thus, the heating medium of the present invention can vary widely. Theegg can be heated with any fluid heat transfer medium or it can beheated by direct heat from heat sources, such as radiant heaters,infrared heaters, or radiation, such as microwaves. However, since allof those direct heating means require special care in ensuring that thedirect heat uniformly heats all surfaces of the egg, it is preferredthat the heating medium is a fluid heat transfer medium, since the fluidcan be caused to flow around the egg and ensure uniform heating alongall surfaces of the shell of the egg. The fluid medium may be any gas,e.g. air, nitrogen, carbon dioxide, etc., but it is preferred that thefluid medium be an aqueous medium, since heat transfer from aqueousmediums is easy to control. Thus, the aqueous medium may be in the formof water vapor, but, more preferably, the aqueous medium is liquidwater. Mixtures or sequences of heating medium may also be used, e.g.water and then air.

However, liquid water does have a disadvantage in that, as is wellknown, during heating in liquid water, gases nucleate on the shell ofthe egg. This can be observed by anyone boiling an egg in a pot. Thenucleated gases decrease the heat transfer between the liquid water andthe shell of the egg and, hence, into the interior of the egg. Sincethis decrease in heat transfer may not be uniform throughout the area ofnucleated gases on the shell of the egg, it is most preferable to avoidor displace those nucleated gases to the extent possible. This may bedone by adding a surface active agent to the water, e.g. a food-gradeionic, anionic or non-ionic surface active agent, many of which areknown in the art, for example, the Tweens. Usually only a fraction of apercent of surface active agent is necessary, e.g. one half of onepercent based on the weight of the water, although the surface activeagent can be as low as one hundredth of a percent and as high as threeor four percent.

Alternatively, the nucleated gases may be displaced from the shell ofthe egg when at least one of the water and the egg is in motion relativeto the other. Thus, the water may be sprayed onto the egg, which keepsthe water in motion relative to the egg, or the egg may pass through asubstantially continuous curtain of flowing water, or in a water bath,the water may be fully circulated over the egg. In addition, in any ofthe above cases, the egg may be rotated on a support, and supports forrotating eggs are well known in the art. Alternatively, both motion ofthe water and the egg can be used, along with a surfactant (non-foamingsurfactant) to minimize or avoid inconsistent heat transfers due tonucleated gases.

As noted above, the present invention relies on controlling thetemperature and dwell time of the yolk of the egg. However, within theentire yolk, the temperatures thereof may vary, depending upon theproximity of a particular portion of the yolk to the shell and theproximity of the particular portion of the yolk to the center of theyolk. As will be explained hereinafter in detail, the present method iscarried out by controlling the temperature of the yolk at a centralportion thereof. The center of the yolk, of course, is a theoreticalpoint and modern temperature-measuring devices are not capable ofmeasuring temperatures at a theoretical point. However, such devices arecapable of measuring temperatures in a central portion of the yolk,consistent with the width of a modern temperature-measuring probe, e.g.thermocouple. Thus, in the present specification and claims, the centralportion of the yolk is defined to mean that portion of the yolksubstantially surrounding the center of the yolk which has sufficientvolume to accommodate and receive a conventional temperature-measuringprobe.

As noted above, it has been found that the temperature of the yolk mustbe in the range of 128° F. to 138.5° F. While pasteurization can beachieved with yolk temperatures as low as 126° F., this temperature isnear the minimum temperature to kill Salmonella and variables, such asparticular egg histories and sizes/grades, etc., as explained below,very significantly affect results. Thus, at 126° F., the results are sovariable as to be unreliable, and to avoid the same, the yolktemperature must be at a higher value, i.e. at 128° F. or higher.

In this regard, experiments which attempted to establish the correlationline of FIG. 1 at between 128° F. and 126° F. showed the data for thatcorrelation line to be so scattered that parameter lines A and B couldnot be established with any certainty. This reflects that attemperatures below 128° F. the above-mentioned variables become sosignificant that pasteurization while retaining functionality cannot beaccurately predicted. Thus, for practical application of the invention,the central portion of the yolk must be at a temperature of 128° F. orhigher.

This means, of course, that when a heat transfer medium as describedabove is used, that medium must be at a temperature of at least 128° F.,since, otherwise, that heating medium would not be capable of heatingthe central portion of the yolk to at least 128° F. On the other hand,while the central portion of the yolk should not reach a temperaturegreater than about 138.50° F., the temperature of the heating medium canbe higher than that temperature, since there will be a temperaturedifferential between the temperature of the heating medium and thecentral portion of the yolk until an equilibrium temperature isestablished. However, it has also been found that a higher temperatureof the heating medium should not be substantially greater than 138.5°F., since, otherwise, the chances of decreasing the functionality of thealbumen before pasteurization occurs, especially near the shell,increases. For this reason, it is preferable that the medium is heatedto temperatures no greater than 142° F.

The medium may be heated to more than one temperature during thepasteurization process. For example, the medium may be heated to ahigher temperature of no greater than 142° F. for part of thepasteurization dwell time of the yolk, and then cooled to lowertemperatures no less than 128° F. for the remainder of the portion ofthe dwell time of the yolk. There are certain advantages to heating tosuch higher temperatures and then cooling to such lower temperaturesduring the pasteurization process, in that the total time required forpasteurization is decreased. At the higher yolk temperatures, withinparameter lines A and B of FIG. 1, the chances of decreased albumenfunctionality are increased. Therefore, in order to decrease processingtime and the chances of decreased functionality, the heating medium maybe heated to higher temperatures for part of the pasteurization and thenheated to a lower temperature for the remaining part of thepasteurization, consistent, of course, with the yolk temperature beingwithin the range specified above and within the dwell times of parameterlines A and B. If such different temperatures of the heating medium areused, it is preferable that the higher temperatures are between about136° F. and 139° F. and the lower temperatures are between about 131° F.and 135° F.

The most preferred method in the foregoing regard is that of using oneor more higher heating medium temperatures, e.g. 138° F., until the yolktemperature reaches a target value, e.g. 134° F., and then decreasingthe temperature of the medium to that target temperature, e.g. 134° F.,and maintaining that reduced medium temperature until the dwell timespecified by FIG. 1 is reached. Several or more different mediumtemperatures may be used, so long as the resulting temperatures anddwell times of the yolk fall within parameter lines A and B of FIG. 1.This provides some latitude in fine adjustment of the process foroptimum pasteurization and retention of functionality of the egg evenwith varying egg input and input egg conditions.

In this latter regard, a difficult problem in the prior art, where theeggs were processed by temperature control of the heating medium alone,e.g. a water bath, for specified time ranges, is that the particularinput eggs and the prior handling conditions thereof could verysubstantially affect the results. For example, freshly laid eggs arenormally stored in controlled temperature refrigerators until handling,processing, packaging and distribution are achieved, with the possibleexception of grading. However, such conditions are not uniform, and theconditions vary from processor to processor. Thus, if eggs to beprocessed according to the prior art were stored at 41° F. and thenplaced in a heated water bath maintained at the prescribed temperaturesand allowed to dwell therein for the prescribed time, the actual resultsthat would be achieved thereby in terms of decrease in microorganismsand preserved functionality would vary significantly from that whichwould be achieved if the eggs had been stored at, for example, 44° F.Those results would vary most considerably if the eggs to be processedwere brought to room temperature before processing. This is because theamount of heat required to be transferred into the egg to achievereduction in microorganisms depends upon the temperature of the eggentering the process, e.g. entering the temperature-controlled hot waterbath.

Likewise, the effects of specific dwell times in a water bath controlledat a specific temperatures will vary with the age of the egg. Inaddition, it will vary with the size, particular configuration, weightand density of the particular egg, which can vary somewhat. At least tosome extent, the effects will vary with the particular breed of poultryused to produce the eggs.

All of these problems are obviated by the present method, where thecontrol for pasteurization and retention of functionality is not inconnection, specifically, with the temperature of the heat transfermedium, but is the result of the control of the temperature of thecentral portion of the yolk of the egg.

However, changes in functionality, especially of the albumen, can occurwhen the time required to reach the target yolk temperature withinparameter lines A and B is overly long. This is referred to as the"come-up" time. The "come-up" time can be minimized by prewarming theeggs, e.g. to room temperature or up to about 120° F., prior toprocessing for pasteurization. It should be noted that any time duringwhich the yolks of the eggs are within parameter lines A and B inreaching such target yolk temperature should be subtracted from thedwell time required by FIG. 1.

In regard to the "come-up" time, it was found that at yolk temperaturesbelow 120° F., the growth rate of Salmonella is very low. Further, itwas found that at yolk temperatures at 120° F. or below, proteindenaturing (loss of functionality) also proceeds at a very low rate.With these two discoveries, it was found that eggs could be prewarmed toyolk temperatures up to 20° F. over relative long times without anysignificant increase in Salmonella or decrease in functionality. Whilethe longer the prewarming time the greater the chance for loss offunctionality and increase in Salmonella, prewarming periods of up totwo hours, especially one hour and more especially up to 30 minutes arequite satisfactory. Such prewarming can considerably reduce the"come-up" time.

As noted above, the present method ensures that a Salmonella species,which may be present in the egg yolk, is reduced by at least 5 logs(base 10 log) while the albumen functionality of the egg, measured inHaugh units, is not substantially less than the albumen functionality ofa corresponding unpasteurized in-shell egg. In this regard, it has beenfound that if a Salmonella species present in the egg is reduced in anamount by at least 5 logs, then any other pathogenic microorganism whichmay be expected to be in the egg will also be reduced by at least 5logs, particularly, when the reduction of 5 logs is in connection withthe species Salmonella enteritidis. Salmonella enteritidis is aparticularly troublesome pathogenic species of Salmonella in that it isa more common species of infection in the yolk of the egg, for thereasons explained above, and is a particularly virulent pathogenicspecies. In addition, that species is more difficult to destroy becauseof its predominant yolk location and the corresponding difficulty todestroy while maintaining functionality. Therefore, if the process isdesigned and carried out so as to reduce Salmonella enteritidis by atleast 5 logs, as essentially the worst case scenario, then it can beassured that other pathogens in the egg have been reduced sufficientlythat the egg is safe for consumption by humans of ordinary health andcondition.

In this regard, FIG. 1 is a graph of the temperature of the centralportion of the yolk of an egg being pasteurized versus the log of thedwell time of the yolk at that temperature. That correlation is astraight line on log scale, and parameter lines A and B show permissibledeviation from that correlation line, while still substantially ensuringa 5 log reduction in a Salmonella species, as well as a substantialretention of the albumen functionality. For optimum results, the dwelltime at a specific temperature or dwell times at different temperatures,as explained above, should fall near that correlation line. However, asnoted above, for some fine tuning of processes in connection with theparticular egg input, the technical ability to control temperatures, andfor shortening the process time, the time-temperature correlation can bewithin parameter lines A and B and satisfactory results will beobtained. However, it is much preferred that deviations from thecorrelation line be at longer dwell times, rather than at shorter dwelltimes, from the correlation line. This will ensure a 5 log reduction ofSalmonella while still ensuring good functionality. Thus, the dwelltimes are within a 95% statistical confidence level for the straightline graph of temperature and log of dwell time (indicated in minutes),where one terminus of the line is at 128° F. for 215 minutes and theother terminus of the line is at 138.5° F. for 8.0 minutes. The 95%confidence level is calculated by standard statistical methods which arewell known to the art and need not be described herein.

Thus, by carrying out the process so that the yolk is pasteurized in theabove manner, this also ensures that the entire mass of the egg islikewise pasteurized such that there is at least a 5 log reduction ofSalmonella species throughout the yolk, albumen and entire mass of theegg.

Newly proposed standards of the United States Food and DrugAdministration (USFDA) require at least a 5 log reduction in Salmonellaspecies for in-shell eggs to qualify as pasteurized. Acceptably retainedfunctionality must also be achieved for practical commercialapplication. Heretofore, the art has not been able to meet that proposedstandard. For example, only a 3 or 3.5 log reduction of a Salmonellaspecies could be achieved by prior art processes, while reliablyretaining the functionality of the in-shell eggs. As a result, some ofthe prior processes, instead, purported to use the USDA standard forliquid eggs (out-of-shell eggs). Those in-shell eggs are, nevertheless,not pasteurized eggs in that, while they may be safer to eat, they arenot safe to eat.

As noted above, while the functionality of an egg can be determined byseveral or more tests, it has been found that the most sensitive andreliable test for determining retained functionality of eggs pasteurizedby the present invention is that of the albumen functionality test.Since the yolk temperature is controlled according to the presentinvention, i.e. controlled at a temperature between 128° F. and 138.5°F., this, inherently, means that the albumen reaches a temperature of atleast 128° F., but could for a portion of the time of the pasteurizationprocess reach temperatures up to 138.5° F. or slightly higher when thetemperature of the heat transfer medium is higher than 138.5° F., e.g.up to 142° F., as explained above. Therefore, these higher temperaturesof the albumen, as opposed to the temperatures of the yolk, can causeloss of functionality of the albumen before there is a substantial lossof functionality of the yolk. By, therefore, controlling the yolktemperature, the functionality of the albumen is safeguarded so as tonot be substantially reduced from that of an unpasteurized egg.Therefore, it can be ensured that the functionality of the whole eggincluding the yolk will not be substantially reduced in functionality.

As a very surprising and unexpected occurrence in connection with thepresent invention, when pasteurization is carried out very close to thecorrelation line of FIG. 1, not only is the albumen functionality notdecreased but, in fact, quite surprisingly, is increased in someregards. The data actually shows that while a correspondingunpasteurized egg of Grade A quality may have an albumen functionalityrating of between 60 and 72 Haugh units, when an egg is pasteurizedclose to the present correlation line of FIG. 1, the albumenfunctionality rises by up to 10 units, e.g. somewhere in the 70 or 80units. It is noticed that there is a slight enlargement of the air sacand an enlargement of the yolk in such eggs, which enlargements areusually found in slightly older eggs. Even when operating the processclose to either parameter line A or parameter line B, the albumenfunctionality of pasteurized Grade A eggs will still exceed 60 Haughunits.

In this latter regard, the term "corresponding unpasteurized in-shellegg" is defined to mean an egg of corresponding shape, weight, age,flock and processing history as that of the pasteurized egg, since, asexplained above, these variables can effect the results of the processand, correspondingly, the results of the Haugh unit test. Therefore, inconnection with the corresponding unpasteurized egg, the pasteurized eggis not substantially reduced in the albumen functionality test.

As is well known in the art, any substantial heating of egg proteincauses some denaturization of that protein. In the prior art processes,while reduction of microorganisms in the eggs could easily be achieved,reduction of higher log cycles resulted in denaturing of the egg proteinand a decrease in the functionality of the eggs to the extent that theeggs were not commercially useful for all purposes. In addition, thatdenaturing of the protein causes very substantial changes in thefunctionality of the eggs with storage. Thus, in those prior artprocesses, while freshly heat-treated eggs might not have acceptablefunctionality for all uses, they might have acceptable functionality forlimited uses, e.g. producing a soft-boiled egg. However, with storage ofthe eggs, which is normal in the industry, even that functionality wouldsubstantially further decrease such that long time stored eggs wouldbecome unacceptable for almost all uses. Therefore, it is not onlynecessary to achieve pasteurization, while retaining functionality, asdescribed above, but it is also necessary to retain that functionalityover a significant period of time of storage of the eggs. Otherwise,without preservation of functionality during storage, the pasteurizedeggs are simply not acceptable from a commercial point of view.

Storage affects both unpasteurized and pasteurized eggs (e.g. stored at41° F.). There is some weight loss during storage, the yolk height andwidth tend to change, yielding a changed yolk index and the whippedalbumen height, in Haugh units, also tends to change in both types.These are, however, usually not practically significant. Generallyspeaking, eggs should not be stored (e.g. at 41° F.) for longer thanabout 75 days prior to use. In the prior art approaches, the processedeggs stored for up to 75 days showed unacceptable changes in eggfunctionality. For example, depending upon the prior art approach, theeggs could not make an acceptable sunny-side up fried egg, acceptablehomogeneous scrambled eggs, or acceptable over-easy fried eggs. Neithercould those eggs be used for making food products, such as saladdressings, e.g. Caesars salad dressing, mayonnaise, sponge cakes,cookies and other baking applications.

While the following example details the data of test results, thatexample shows that the present process not only destroys the Salmonellaspecies so as to pasteurize the egg, i.e. at least a 5 log reduction,but does so without substantially adversely affecting the egg quality,e.g. functionality, even when stored up to 75 days at 41° F. Those eggscan be used for preparing sunny-side up, scrambled and over-easy cookedeggs, as well as in preparing salad dressings, mayonnaise, sponge cakes,cookies and other baking applications.

Thus, the present method and pasteurized eggs are further different fromprior art methods and treated eggs in that the present pasteurized eggshave an egg weight substantially the same as a correspondingunpasteurized egg, a yolk index and yolk strength substantially the sameas a corresponding unpasteurized egg, and an angel cake test and asponge cake test substantially the same as a corresponding unpasteurizedegg. Further, the present pasteurized eggs have frying, scrambling andboiling characteristics substantially the same as a correspondingunpasteurized egg, and, just as importantly, those characteristics aremaintained in the present pasteurized eggs for up to 75-days storage at41° F.

The egg produced by the method of the invention, as noted above, is apasteurized in-shell chicken egg which comprises a pasteurized centralportion of the yolk of the egg having at least a 5 log reduction of aSalmonella species which may be present in the egg in its unpasteurizedform. The egg has an albumen functionality, measured in Haugh units, notsubstantially less than a corresponding unpasteurized in-shell egg. Inthis regard, "not substantially less" means that any differences are notof practical significance. The present pasteurized egg also has thereduction in Salmonella species throughout the yolk and albumen of theegg. Also, the egg weight, the yolk index, the yolk strength, the angelcake test, the sponge cake test, and frying, scrambling and boilingcharacteristics of the present pasteurized egg are not substantiallyless than a corresponding unpasteurized in-shell egg. Likewise, thepresent pasteurized egg can substantially maintain those characteristicsfor up to 75-days storage at 41° F.

It will be appreciated by those skilled in the art that a reduction inSalmonella species of at least 5 logs, while not substantiallydecreasing the albumen functionality, is a very substantial improvementin the art. Prior art approaches, such as those described above, underideal conditions, could produce, perhaps, as much as a 3.5 log reductionin Salmonella enteritidis without substantially decreasing the albumenfunctionality. However, while up to a 3.5 log reduction will make theegg safer to eat, that egg is not pasteurized according to the proposedUSFDA standard, discussed above, and, hence, cannot be said to be safelyconsumable by a human of normal health and condition. Unless at least a5 log reduction is obtained, under the proposed USFDA standard, itcannot be assured that the egg can be safely consumed by such human. Thepresent process is able to achieve that 5 log reduction, whilemaintaining the functionality of the egg, and, in this sense, has solvedthe dilemma which has plagued the art for some time. Indeed, byfollowing closely the correlation line of FIG. 1, log reductions greaterthan 5 can be achieved, while substantially maintaining thefunctionality, e.g. 6 log reductions and even 7 log reductions, and thisis a very substantial advance in the art.

While, as stated above, the method may be carried out by heating theeggs with any desired means, as also stated above, the preferred methodis that of heating the eggs in an aqueous medium, preferably in a waterbath, for the reasons set forth above, and this particular means ofheating the eggs will be specifically discussed, for concisenesspurposes, but it is to be understood that the invention is not limitedthereto. It should be further understood that the specific methodillustrated below is merely a preferred method when using a water bathas the heating medium, but that other methods may be used in connectionwith the use of a water bath as the heating medium, or in connectionwith other heat transfer media, so long as the yolk temperature/dwelltime of the invention is observed.

In carrying out the method, it is necessary to control the yolktemperature of the egg. However, it is first greatly preferred toappropriately calibrate a particular apparatus and particular processconditions of that apparatus to ensure that the particular apparatus andconditions calibration results in the required yolk temperature/dwelltime to pasteurize the eggs and retain functionality, according toFIG. 1. Thereafter, subsequent processing and pasteurization of eggs canbe achieved by repeating those calibration process conditions withoutmeasuring the yolk temperature/dwell time of the eggs. For example, insuch calibration, it may be established by temperature measurement ofthe yolk that when eggs stored at 41° F. are placed in a water bath at137° F. for a particular apparatus with a particular agitation for 14minutes and then removed and cooled in 41° F. storage, the yolktemperature/dwell time required by FIG. 1 is achieved. Thereafter, toeffect pasteurization of succeeding lots of eggs, including the requiredyolk temperature/dwell time and retained functionality, it is onlynecessary to maintain that calibration agitation, water temperature,14-minute dwell time, egg storage temperature and cooling temperature,to ensure that the yolk temperature/dwell time is that required by FIG.1, without having to measure that yolk temperature/dwell time orfunctionality of succeeding lots of eggs. However, it is preferable thatthe calibration be periodically rechecked during processing ofsucceeding lots of eggs by checking the calibration with a lot of eggsfrom time to time by measuring the temperature of the yolk and measuringfunctionality.

To these ends, for a chosen lot of eggs being pasteurized, a statisticalnumber of the eggs being processed will have a temperature probeinserted into that central portion of the yolk, and these eggs may bereferred to as "control eggs". The temperature probe, e.g. thermocouple,is inserted into the egg, in a manner well known in the art, and sealedthereagainst by conventional manners, e.g. glues, waxes, putties, andthe like, to prevent water from entering the egg during processing. Thetemperature of the central portion of the control egg yolks is monitoredby the temperature probe, and the yolk temperature/dwell time isdetermined and controlled to ensure that the values fall withinparameter lines A and B of FIG. 1. If so, the calibration has beenobtained or maintained; if not, adjustment of operating conditions andrecalibration are required.

Whether in regard to such calibration or in regard to productionpasteurization of eggs, normally, eggs of essentially the same sizerange will be processed as a lot. Otherwise, with eggs of greatlydifferent sizes, the calibration or production processing could notensure pasteurization. The sizes may be determined by weight, and, forexample, eggs of a target weight plus or minus 10% are processed as alot.

In the method of the invention, a lot of eggs is placed in aconventional pasteurization apparatus, which may be any conventionalpasteurization apparatus, such as a cheese vat, and heated water isintroduced into that vat with the water being heated to at least 128° F.and up to 142° F., but preferably less than 138.5° F. The temperature ofthe central portion of the egg yolk of a statistical number of eggs ismonitored by a temperature probe present in "control" eggs as a periodicor continual recheck of calibration, as explained above, or as theprimary means of control of egg yolk temperature, e.g. in an apparatuswhich has not been calibrated as described above. Preferably, however,the apparatus has been calibrated, and such control eggs are notrequired or are used only periodically to recheck calibration. When thedesired target temperature of the yolk, e.g. 134° F. is reached, thetemperature of the water is controlled to maintain that targettemperature by adding cold or hot water as required, and that yolktemperature is controlled for the time set by the correlation line ofFIG. 1 or at least within parameter lines A and B.

After the eggs have reached that temperature and been controlled at thattemperature for the time of the correlation line, the eggs are removedfrom the pasteurizer and cooled to at least below 126° F., and morepreferably below 115° F., and yet more preferably below 100° F. Thiscooling should be as rapid as possible such that residual temperaturesin the eggs do not substantially further denature protein beyond thatachieved at the correlation temperature. Usual cooling procedure, e.g.air, is sufficient for this purpose, but it is preferable to cool theeggs in cool water or in normal storage, e.g 41° F., after removal fromthe pasteurizer. It should be noted that any time during which the yolksof the eggs remain within parameter lines A and B during cooling shouldbe subtracted from the dwell time required by FIG. 1. After the eggshave been so cooled, the eggs are then dried, e.g. air drying, packagedand transferred to a cold storage, maintained at an acceptabletemperature of between 38° F. and 45° F., e.g. 41° F., and are thenready for distribution.

In addition, for calibration, recheck of calibration or primary controlof the pasteurization, a statistical number of "control" eggs may beanalyzed for functionality. While the functionality will be largelyknown by the albumen functionality test, in Haugh units, to ensure thatthe functionality of the pasteurized egg is substantially the same as acorresponding unpasteurized egg, in addition to the albumenfunctionality, "control" eggs may be examined for egg weight, yolk indexand yolk strength, angel cake test and sponge cake test, as well as thecharacteristics of frying, scrambling and boiling, as described above.

All of the control eggs, i.e. yolk temperature and functionality controleggs, are essentially part of calibration for a particular pasteurizingapparatus operated at particular conditions with particular eggs. Thisis because particular pasteurizing apparatuses can vary in theirperformance of pasteurization, and any particular apparatus must becalibrated to ensure that the yolk temperature/dwell time reaches thedesired results required by FIG. 1. However, as noted above, oncecalibrated, for successive pasteurizations of substantially the sameeggs, then it is no longer necessary to use the temperature probed"control" eggs or to perform the functionality tests mentioned above,since by repeating the calibration process, the same results will beachieved. This is, of course, based on the assumption that allsucceeding lots of eggs processed in that same manner have essentiallythe same histories and conditions, as described above. If the historiesor conditions change markedly, then the apparatus must be recalibrated,as discussed above.

Optionally, the pasteurized eggs may be protected from environmentalrecontamination by wrapping the eggs or cartons of eggs in a protectivebarrier, such as a plastic film. Heat shrinkable plastic film isparticularly well suited to this purpose, such as the heat shrinkablefilms made by the Cryovac Division of W. R. Grace & Co. These films areco-extruded polyolefin films, some of which are cross-linked. Thesefilms are generally referred to as "industrial food source films" andparticularly useful are those films designed as D-955 and MPD 2055. Itis to be understood, however, that pasteurization of eggs, similar topasteurization of milk, does not extend the shelf life of the eggs nordoes it lessen the necessity for proper handling and cooling of theeggs, in the same manner as pasteurized milk. Accordingly, simplywrapping each individual egg or package of eggs will not extend theshelf life of the eggs.

The invention will now be illustrated by the following example, whereall percentages and parts are by weight, unless otherwise indicated.

EXAMPLE

This example illustrates two different protocols for pasteurizing eggs.

In a manner described above in connection with the method of calibratinga particular apparatus/process conditions, the graph of FIG. 1 wasexperimentally determined by inoculating a statistical number of eggswith Salmonella enteritidis. The inoculated eggs were sealed in the samemanner as sealing the temperature probe of the "control" eggs. These"control" inoculated eggs were processed in the same manner. The"control" inoculated eggs were examined for Salmonella enteritidis logreduction by standard microbiological techniques. The graph of FIG. 1was then constructed on the basis of yolk temperature/dwell time whichwould achieve at least a 5 log reduction in Salmonella enteritidis.Parameter lines A and B show a 95% confidence level. Retainedfunctionality was confirmed by the same procedure described below.

Thus, it was known by this experimental data that by processing eggswithin parameter lines A and B of FIG. 1, a 5 log reduction in aSalmonella species resulted while maintaining functionality. ThisExample, therefore, illustrates that retained functionality and furtherillustrates that retained functionality during long-term storage, i.e.at 41° F. for up to 75-days storage.

The pasteurizer used in this example was a Kusel (Kusel Equipment Co.,Watertown, Wis.). It has a 100 gallon capacity and is usually used as acheese vat. The vat is filled with water and heated to the targettemperature with a steam jacket. The vat is equipped with a Nonoxsteam/water mixer and that target temperature is maintained by flowingtemperature controlled water into the vat with a corresponding outflowof water. For temperature control, the vat is equipped with mountingsfor separate temperature probes to monitor the water temperature. Inthis example, the water temperature was monitored using three Type T 24gauge (copper-constantant Teflon-coated) thermocouples connected to aCole-Palmer (Niles, Ill.) Dual Input Thermocouple Thermometers (ModelNo. 08112-20). The thermocouples were placed at three differentlocations and at three different water levels throughout the vat tomonitor the evenness of water temperature.

Thirty-six eggs were used in each test and were placed in conventionalfiller flats at 12 inches below the water level. Each batch of test eggsalso contained three eggs that were probed with a thermocouple. Thethermocouple was inserted 13/4 inches into the large end of the eggs tothe central portion of the yolks. The eggs were sealed with a gel-basedglue and allowed to dry. Temperatures of the eggs and water vat weremonitored at one minute intervals with an accuracy of ±0.2° F. Mildagitation was carried out in the vat and was regulated using a rotarystainless steel impeller pump with a 11/2 inch inlet and a 11/2 inchoutlet.

Approximately 4-day old eggs were used for each of the tests, and theeggs were large Grade A quality eggs from the same flock. The eggs hadbeen stored at 41° F. until processed. The eggs were removed from thestorage cooler and placed into the plastic filler flats. The three eggswith the thermocouples mounted therein were also included in each flat.The filler flat was then placed in the preheated vat, and thetemperatures of the water and the egg yolk temperatures were recorded atone minute intervals.

In one protocol, when the average internal yolk temperature of the threeeggs reached 134° F., cool water was added to the vat and mixed, asneeded, to maintain that internal yolk temperature. In the otherprotocol, the cool water was added when the average internal temperatureof the yolk reached 133° F. Both of the protocol fall within parameterlines A and B of FIG. 1.

After processing, the eggs were removed from the water vat and placeddirectly into a 41° F. cooler, by which they were rapidly cooled.

No pasteurized eggs were removed from the cooler until after the averageinternal yolk temperature reached 41° F. The various batches for eachtreatment were combined and randomly assigned to Day 0, 10, 20, 30, 60or 75 days storage.

Treatment of the eggs were assigned treatment numbers as follows:

1. Treatment No. 1--a control group of unpasteurized eggs;

2. Treatment No. 2--a control group of unpasteurized eggs which wereplaced in a Cryovac package (film);

3. Treatment No. 3--pasteurized eggs, initial water bath temperature of137° F. and average internal yolk temperature of 133° F.;

4. Treatment No. 4--pasteurized eggs, initial water bath temperature of137° F. and average internal yolk temperature of 133° F., packagedwithin a Cryovac package;

5. Treatment No. 5--pasteurized eggs, initial water bath temperature of138° F. and average internal yolk temperature of 134° F.; and

6. Treatment No. 6--pasteurized eggs, initial water bath temperature of138° F. and average internal yolk temperature of 134° F., packagedwithin a Cryovac package.

Treatment Nos. 2, 4 and 6 were packaged in groups of six in cardboard orplastic filler flats. The packaging was provided by Cryovac andconsisted of a plastic sleeve into which the eggs were placed and thensealed using a bar sealer. The plastic sleeve was made of Cryovac D-955film.

A description of the tests of the various treatments at day intervals isset forth in Table 1 below.

                  TABLE 1                                                         ______________________________________                                        Day      Treatment Tests                                                      ______________________________________                                        0        #1, #3, #5                                                                              Egg Quality -  Weight                                                                        Yolk Index                                                                    Haugh Units                                                    Yolk Strength                                                                 Foam Stability                                                                Angel Cake Volume                                                             Sponge Cake Volume                                                            Whip Test                                                                     Lysozyme Activity                                          10 & 20  #1, #2, #3,                                                                             Egg Quality -  Weight                                               #4, #5, #6               Yolk Index                                                                    Haugh Units                                                    Yolk Strength                                              30, 60 & 75                                                                            #1, #2, #3,                                                                             Egg Quality -  Weight                                               #4, #5, #6               Yolk Index                                                                    Haugh Units                                                    Yolk Strength                                                                 Foam Stability                                                                Angel Cake Volume                                                             Sponge Cake Volume                                                            Whip Test                                                                     Lysozyme Activity                                          ______________________________________                                    

A. Egg Quality Tests:

1. Egg Weight--Initial and final egg weights (to one hundredth of agram) were recorded to determine if a weight gain or loss occurredduring processing or storage.

2. Yolk Index--Yolk index is a measure of yolk quality. A decreasingyolk index indicates a lower yolk quality. ##EQU1##

3. Haugh Units (Albumen Functionality Test)--The Haugh units measurealbumen (egg white) quality. As the egg ages, the thick white thins. TheHaugh units are calculated using both the egg weight and the height ofthe thick albumen. Standard Haugh unit values for different grades ofeggs are as follows:

    ______________________________________                                        Grade AA          >72 Haugh units                                             Grade A           60-72 Haugh units                                           Grade B           <60 Haugh units                                             ______________________________________                                    

4. Yolk Strength--Yolk strength is a measure of how easily the yolk willbreak when dropped from a distance of 6 inches onto a flat surface.

B. Properties Tests:

1. Angel Cake Volume--Angel cake volume is a sensitive test of egg whiteprotein damage. Generally, heat damage will greatly increase whippingtime and decrease the cake volume.

2. Sponge Cake Volume--Measures both foaming volume and emulsificationproperties. The yolk proteins are less heat sensitive than egg whiteproteins. Sponge cake volume provides a measure of the effect of heatprocessing on yolk functionality.

3. Foaming Stability--Measures the foaming efficiency of egg whites. Thefoaming properties of egg whites are provided by certain egg whiteproteins.

These proteins are particularly sensitive and may be damaged by heatprocessing. If proteins are damaged, then foam volume will decrease andthe liquid drainage from the whipped foam will increase. The egg whitesare whipped to a specific gravity of 0.1. Percent drainage wascalculated by dividing the grams of drainage by the initial weight ofthe foam.

4. Whip Test--This is another measure of the foaming efficiency of eggwhites. Egg whites are whipped for a specific time and speed and theheight of the foam is then measured.

All functionality tests were performed in triplicate per treatment.

C. Other Tests:

1. Lysozyme Test--This test measures the enzyme activity. Lysozyme isone of the constituents in eggs which provides some antibacterialactivity. It acts upon gram positive organisms. Rate of clearing wasdetermined per minute at the most linear portion of the curve, i.e.between 0.5-3.0 minutes.

Results and Observations of Eggs at Day 0

Visual Observations

Observations were conducted on eggs from Treatment Nos. 1, 3 and 5.Treatment No. 1 (unpasteurized eggs) showed no signs of cloudiness, andthe yolk shape was normal. Treatment No. 3, pasteurized with an initialwater bath temperature of 137° F. and a yolk temperature of 133° F.(137-133° F.) showed cloudiness in the thick and thin albumen. The yolkwas slightly flatter than in Treatment No. 1. Treatment No. 5 (138-134°F.) was very similar in appearance to Treatment No. 3, with theexception of a slight decrease in cloudiness in the thin albumen.

Egg Quality

Weight Loss--No statistically significant (p>0.05) differences in weightloss occurred between the control and pasteurized eggs at Day 0. Astatistically significant (p<0.05) difference was found between thepasteurized eggs, with the eggs from Treatment No. 3 (137-133° F.)losing the least amount of weight.

Yolk Index--No statistically significant (p>0.05) differences in yolkindex occurred between Treatment Nos. 1, 3 and 5.

Yolk Strength--Pasteurization did not statistically significantly(p>0.05) affect yolk strength.

Haugh Units--No statistically significant (p>0.05) differences in Haughunits occurred between Treatment Nos. 1, 3 and 5.

Properties Test

Angel Cake Volume--Differences in angel cake volume between all threetreatments were not statistically significant (p>0.05). However,whipping time to achieve a medium peak was increased in the pasteurizedeggs compared to the control eggs.

Sponge Cake Volume--Significant (p<0.05) differences were found insponge cake volume between Treatment Nos. 3 and 5, with Treatment No. 3having greater cake volume. There was not a statistically significant(p>0.05) difference in sponge cake volume between the control andpasteurized eggs.

Whip Test--Whip test results indicated a statistically significant(p<0.05) difference between the control and pasteurized eggs with thecontrol eggs having the least amount of drainage and the greatest foamvolume. There was no statistically significant (p>0.05) differencebetween Treatment Nos. 3 and 5. To achieve a specific gravity of 0.1 inthe control eggs, the whipping time was 30 seconds compared to 3 minutesfor the pasteurized eggs.

Other Tests

5 Lysozyme--A statistically significant (p<0.05) difference in lysozymeactivity was found between the control and pasteurized eggs. Differencesin enzyme activity between Treatment Nos. 3 and 5 were not statisticallysignificant (p>0.05).

Conclusion

At Day 0, the pasteurized eggs exhibited some cloudiness in the thickalbumen (white) as compared to unpasteurized eggs. The degree ofcloudiness is not practically significant.

A small amount of weight was lost during the pasteurization process butwas comparable to average weight loss in the unpasteurized eggs. Noweight gain occurred during pasteurization. The pasteurization processdid not practically significantly adversely affect the yolk index, Haughunits, or yolk strength. After pasteurization, the eggs remained largeGrade A quality eggs.

Pasteurization did not practically significantly affect angel and spongecake volume when comparing to the unpasteurized egg. However, TreatmentNo. 3 (137-133° F.) had a greater sponge cake volume than Treatment No.5 (138-134° F.), which was found to be significant.

Unpasteurized eggs were slightly superior in foam volume and foamstability as compared to the pasteurized eggs, but this superiority isnot practically significant.

Lysozyme activity decreased in the pasteurized eggs as compared to theunpasteurized eggs. However, the loss in activity is of little practicalsignificance.

Results and Observations of Eggs at Day 10

At Day 10, the results were similar to Day 0 in regard to the commontests. Cloudiness was apparent in the pasteurized eggs compared to theunpasteurized eggs. The degree of cloudiness is not practicallysignificant. No visual differences were observed between the packagedand unpackaged eggs.

Some degree of weight loss occurred in all treatments during the 10-daystorage period. Packaging did not significantly affect the amount ofweight loss.

A statistically significant difference was found in yolk index betweenthe pasteurized and unpasteurized eggs and the packaged and unpackagedeggs. Haugh units were not affected by the pasteurization process.Unpackaged eggs had higher Haugh units as well as eggs from TreatmentNos. 5 and 6. The differences in the yolk index and Haugh units are notpractically significant and do not affect the quality of the eggs. Theeggs were still large Grade A quality eggs.

Results and Observations of Eggs at Day 20

At Day 20, the results were similar to Day 10 in regard to the commontests. The pasteurized eggs at Day 20 were still cloudy in appearance ascompared to the unpasteurized eggs. Some cloudiness also appeared in thethin albumen. The degree of cloudiness is not practically significant.Packaging did not affect the visual appearance of the eggs.

All treatments lost weight at Day 20 of storage. Packaging did decreasethe amount of weight loss as compared to the unpackaged eggs. Theunpasteurized eggs lost less weight compared to the pasteurized eggs.The amount of weight loss is not practically significant and would notchange the grade designation.

The unpasteurized eggs had a slightly higher yolk index. Packaging didnot affect yolk index. No practical significant differences in Haughunits or yolk strength were apparent between all treatments. At the endof 20-days storage, all eggs were still large Grade A quality eggs.

Results and Observations of Eggs at Day 30

At Day 30, the results were similar to Day 20 in regard to the commontests. Cloudiness in the thick albumen and slight cloudiness in the thinalbumen were present in the pasteurized eggs. The pasteurized eggs werealso slightly more runny in the outer thin albumen than unpasteurizedeggs. No differences between the packaged and unpackaged eggs wereapparent. The degree of cloudiness and runniness is not practicallysignificant.

Weight loss occurred in all treatments, with the unpasteurized eggslosing the least amount of weight. Packaging did not have a significanteffect on weight loss. Unpackaged eggs had a higher yolk index thanthose that were packaged. Packaging and pasteurization did not have asignificant effect on yolk strength or Haugh units. The eggs stillremained large Grade A quality eggs after 30 days of storage.

Angel cake and sponge cake volume was not affected in all treatments atDay 30. Longer whipping times were necessary for the pasteurized eggs.Packaged and pasteurized eggs had a greater sponge cake volume but werenot practically superior to the other treatments.

Foam stability and volume were greatest in the unpasteurized eggs.Longer whipping times were necessary in the pasteurized eggs. Loss oflysozyme activity occurred in all treatments; however, the loss inactivity is of little practical significance. None of these differenceswere of practical significance.

Results and Observations of Eggs at Day 60

At Day 60, the results were similar to Day 30. The cloudiness of thethick albumen and slight cloudiness in the thin albumen of thepasteurized eggs were observed. Packaging did not play a significantrole in appearance. The outer thin albumen of pasteurized eggs wasslightly more runny than the unpasteurized eggs. The degree ofcloudiness and runniness of the pasteurized eggs is not practicallysignificant.

Weight loss occurred in all treatments but was not significantlyaffected by packaging or heat treatments. Weight loss was notsignificant enough to change the classification of the eggs.

Yolk strength and yolk index were not affected by pasteurization orpackaging. Haugh units were greater in pasteurized eggs thanunpasteurized eggs. At the end of 60-days storage, all treated eggs werestill large Grade A quality eggs.

Unpasteurized eggs had greater angel and sponge cake volume. Packagingdid not play a significant role in cake volume. Foam stability andvolume were greater in the unpasteurized eggs. Longer whipping timeswere needed for the pasteurized eggs. None of these differences werepractically significant.

Lysozyme activity was lost in all treatments but was not practicallysignificant.

Results and Observations of Eggs at Day 75

At Day 75, the results were similar to Day 60. The pasteurized eggalbumen was more cloudy than that of unpasteurized eggs. The degree ofcloudiness is not practically significant. Runniness was more apparentin the outer thin albumen. Packaging did not appear to make asignificant difference in egg quality.

Weight loss occurred in all treatments, with the packaged eggs losingthe least amount of weight. Yolk index was better in the unpasteurizedeggs. Yolk strength was not significantly affected by pasteurization orpackaging. Haugh units were greater in the pasteurized eggs than in theunpasteurized eggs. However, at the end of Day 75, all treatments werestill large Grade A quality.

Angel cake volume was not significantly affected by pasteurization orpackaging. Unpasteurized and unpackaged eggs had the greater sponge cakevolume. None of these differences are of practical significance.

Foam stability and volume were superior in the unpasteurized eggscompared to pasteurized eggs. Longer whipping times were required forthe pasteurized eggs. None of these differences were of practicalsignificance.

Lysozyme activity decreased in all treatments after 75 days of storage,but not enough to cause a practical significant effect.

Overall Conclusion

Cloudiness of the thick albumen occurs in pasteurized eggs that is notapparent in the unpasteurized eggs. However, the degree of cloudiness isnot practically significant. Cloudiness remained essentially constantduring the 75-day test period and is similar to the natural cloudinessof two-day old eggs.

Weight loss statistically significantly (p<0.05) increased duringstorage for all treatments. Packaging statistically significantly(p<0.05) reduced weight loss of all three treatment groups. Pasteurizedeggs were noted to have statistically significantly (p<0.05) more weightloss as compared to unpasteurized eggs. None of these differences,however, are of practical significance.

Yolk index of the control eggs was found to be statisticallysignificantly (p<0.05) better than the pasteurized eggs for most of thestorage periods. Yolk index statistically significantly (p<0.05)declined in all groups up to 60 days. All treatments exhibited anincrease in yolk index at 75 days, which resulted in a statisticallysignificant (p<0.05) day by treatment interaction. This increase is,however, not practically significant.

The yolk breakage test indicated that yolk breakage was satisfactory inall groups throughout the storage study.

Haugh units of pasteurized eggs were observed to be statisticallysignificantly (p<0.05) higher than the control eggs. This wasparticularly true at longer storage periods (beyond 30 days). Packagingstatistically significantly (p<0.05) improved the Haugh units of alltreatment groups.

Angel cake volume was found to be variable. Control eggs were found tohave a statistically significantly (p<0.05) better angel cake volume.Whip foam volume and foam stability were statistically significantly(p<0.05) superior in control eggs as compared to pasteurized eggs. Noneof these differences are, however, practically significant.

Sponge cake volume was statistically significantly (p<0.05) better inpasteurized eggs up to 30 days as compared to control eggs. After 30days, the control group eggs were noted to have statisticallysignificantly (p<0.05) better sponge cake volume. The 137° F. treatmentgroups eggs were found to have a statistically significantly (p<0.05)better sponge cake volume as compared to the 138° F. treatment group.Although sponge cake volume was variable and declined through storage,the sponge cake volume was acceptable in all tests, and the differencesare not practically significant.

Lysozyme activity statistically significantly (p<0.05) declined in alltreatment groups throughout storage. Pasteurization also statisticallysignificantly (p<0.05) reduced lysozyme activity. Previous research hasshown that lysozyme activity in shell eggs will decrease during storage.Although lysozyme activity was lower in pasteurized eggs, thisdifference is not practically significant.

The pasteurized eggs are suitable for all forms of food preparation.They can be prepared sunny-side up, scrambled and over-easy. Thepasteurized eggs can also be utilized in salad dressings (e.g. Caesarssalad), mayonnaise, sponge cakes, cookies and other baking applications.

Thus, overall, there was no practical significant difference infunctionality of the pasteurized eggs as compared with correspondingunpasteurized eggs for the entire storage period.

Test Details Sponge Cake Test

    ______________________________________                                        Ingredients:   50.0 g  cake flour                                                            46.25 g sucrose                                                               19.30 g dextrose                                                              5.0 g   nonfat dry milk                                                       1.25 g  salt                                                                  2.50 g  baking powder                                                         29.49 g whole egg                                                             18.90 g water (first addition)                                                10.26 g water (second addition)                                ______________________________________                                    

Procedure:

1. Preheat oven to 375° F.

2. Allow all ingredients to come to room temperature.

3. Sift all dry ingredients.

4. Blend all dry ingredients for one minute on the stir speed of aKitchen Aid Mixer (Model K4-B).

5. Add egg to mixture.

6. Mix for 1 minute at speed 2 while slowly adding the first water.

7. Scrape down sides of bowl.

8. Mix for 2 minutes at speed 8.

9. Mix for 2 minutes at speed 4, while slowly adding the second water.

10. Scrape down sides of bowl.

11. Mix 2 minutes at speed 8.

12. Measure out 150 g into a tared 5.5"×3.5"×2.75" baking pan. (Two 1"strips of wax paper placed lengthwise along the bottom of the pan,extended over the ends to facilitate removal of the cake from the pan.)

13. Bake in reel-oven for 30 minutes.

14. After baking, allow to cool for 10 minutes, and remove from pan.

15. Volume determinations are made with a rape seed displacement method.Record initial volume of rape seeds. Turn mechanism over and add cake.Invert mechanism to allow rape seeds to surround cake and record finalvolume.

16. Report results as cm³.

Angel Cake Test

    ______________________________________                                        Ingredients: 90.0 ml blended egg white                                                     1.8 g   salt-cream of tartar mixture                                                  (0.45 g salt, 1.35 g cream of                                                 tartar)                                                               69.0 g  super-fine sugar                                                      56.0 g  flour-sugar mixture                                                           (23.0 g sugar, 33.0 g flour)                             ______________________________________                                    

Procedure:

1. Preheat oven to 390° F.

2. Warm Kitchen Aid Mixer (Model K4-B) by letting it run at speed 10 for15 minutes.

3. Sift twice, separately:

56.0 g flour-sugar mixture

69.0 g sugar

1.8 g salt-cream of tartar mixture

4. Place 90.0 ml blended egg white in a bowl, sift salt-cream of tartarmixture over egg white.

5. With mixer set on speed 10, white to a medium peak.

6. Sift 69.0 g super-fine sugar over foam in three increasingly largerportions and whip at speed 6 for 4 seconds after each addition.

7. Sift 56.0 g of flour-sugar mixture onto foam in 3 portions, foldingafter each addition. Use a wire whip and about 20 strokes.

8. Weight out 120 g of the batter into a tared 5.5"×3.5"×2.75" pan (two1" strips of wax paper placed lengthwise along the bottom of the pan,extended over the ends to facilitate removal of the cake from the pan)with perpendicular sides. Place in reel oven for 20 minutes.

9. Remove from the oven and place in an inverted position on a coolingrack.

10. After 24 hours, measure and record cake volume, using the rape seeddisplacement method. Record initial volume of rape seeds. Turn mechanismover and add cake. Invert mechanism to allow rape seeds to surround cakeand record final volume.

11. Report results as cm³.

Foaming Stability Test

Procedure:

1. Weigh out 50 gram sample of room temperature egg white. Place inmixing bowl (Kitchen Aid Mixer, Model K4-B). Add 10 ml of distilledwater.

2. Begin timing and whip at high speed (speed 10) until the foam has aspecific gravity of approximately 0.1. Specific gravity determination:density determination is substituted, tare a container of known volume,fill, level and weigh. Density is determined by: ##EQU2## The whippingtime for this stage to be reached is noted.

3. Transfer the foam to a tared glass funnel and immediately recordweight of the foam.

4. Cover the funnel with a large petri plate and allow to drain into agraduated cylinder tared on a scale.

5. Record weight of drainage at 15 minute intervals for 1 hour.

Calculation: Calculate grams of drainage per 100 grams of foam from thetotal weight of foam and the weight of drainage by: ##EQU3##

Whipping Test

Procedure:

1. Weigh out 50 gram sample of room temperature egg white. Place intomixing bowl (Kitchen Aid Mixer, Model K4-B).

2. Mix for 90 seconds on speed 2.

3. Mix for 90 seconds on speed 10.

4. Transfer foam from bowl into 600 ml beaker. Level foam and measuredepth of foam.

5. Record results in cm.

Lysozyme Assay

    ______________________________________                                        Reagents:                                                                     ______________________________________                                        0.0667 M     Sodium Phosphate Monobasic:                                                   Dissolve 9.218 g NaH.sub.2 (PO.sub.4) H.sub.2 O and                           bring to 1 L final volume.                                       0.0067 M     Sodium Phosphate Dibasic:                                                     Dissolve 9.48 g Na.sub.2 HPO.sub.4 and bring to                               1 L final volume.                                                M/15         Phosphate Buffer pH 6.2:                                                      Mix portions of 0.0667 M Sodium                                               Phosphate Mono and Dibasic solutions                                          together until a pH 6.2 is reached.                                           About 300 ml of dibasic to 1 L                                                monobasic.                                                       50 mg %      Suspension of U.V. Killed and                                                 Lyophilized Micrococcus                                                       Lysodeikticus: Dissolve 0.5 g in                                              M/15 phosphate buffer pH 6.2 and                                              bring to 1 L final volume. Keep                                               refrigerated at 4° C.                                     ______________________________________                                    

Procedure:

Allow preblended egg white samples and cell suspension to come to roomtemperature. Use plastic as lysozyme adheres to glass.

Dilute egg white samples to give a moderate clearing rate. Add 0.02 mlof egg white to 0.98 ml buffer, gives a theoretical lysozymeconcentration of 70 ug/ml, the limits of this assay are 0.1 to 10 ug(per 2.9 ml substrate) of active lysozyme.

Using the kinetics software package on a Beckman Spectrophotometer, editprogram to the following:

Wavelength=450 nm

Tabulate=1.0 (yes)

Int Time=3.00 sec

Total Time=8.00 min

Plot=1.0

Span=0

Slope=1

Results=1

Factor=1.000

Calibrate using 2.9 ml of cell suspension.

Place cuvette containing 2.9 ml of 50 mg % cell suspension into cellholder in spectrophotometer. Add 0.1 ml of diluted egg white andimmediately mix using a plastic pasteur pipet. Allow program to run.

Maximum velocity will be extrapolated from the most linear portion ofthe curve by the software package. Factors used are 2-8 min., 2-4 min,3-8 min., and 0.5-3 minutes. Rate reported per minute by software.

Report as delta abs (at 450 nm)/min. per g sample/2.9 ml substrate at22° C. (room temperature).

From the above example, it can be seen that the invention provides amethod for, and a pasteurized egg resulting therefrom, reducing aSalmonella species that may be present in eggs by at least 5 logs, whileat the same time does not substantially practically decrease thefunctionality of the pasteurized egg. This is a most significant advancein the art. From the foregoing, it will be understood that the term"pasteurized" in connection with the present invention means that aSalmonella species which may be present in a chicken egg is reduced byat least 5 logs, the pasteurized egg is safe for consumption by humansof ordinary health and condition, and the functionality of the egg,measured in Haugh units, is not substantially less than that of acorresponding unpasteurized chicken egg. In this latter regard, the term"substantially less" does not mean there is no statistically significantdifference, but means that there is no practical difference in terms ofusual uses of the eggs, e.g. in baking, cooking, frying, boiling,poaching, scrambling, etc. The specification and claims should thus beso construed.

It also should be understood that the invention is not limited to theforegoing embodiments, but extends to the spirit and scope of theannexed claims.

What is claimed is:
 1. A pasteurized in-shell chicken egg, comprising apasteurized central portion of a yolk of the egg having at least a 5 logreduction in a Salmonella species present in the yolk and albumen in itsunpasteurized form, said egg having an albumen functionality measured inHaugh units not substantially less than the albumen functionality of acorresponding unpasteurized in-shell egg and a yolk index and yolkstrength substantially the same as a corresponding unpasteurized egg. 2.The egg of claim 1, wherein the Salmonella species is Salmonellaenteritidis.
 3. The egg of claim 1, wherein the albumen functionality isat least 60 Haugh units for a Grade A egg.
 4. The egg of claim 1,wherein the pasteurized egg has an egg weight substantially the same asa corresponding unpasteurized egg.
 5. The egg of claim 1, wherein thepasteurized egg has a result of an angel cake test and sponge cake testsubstantially the same as a result of a corresponding unpasteurized egg.6. The egg of claim 5, wherein the pasteurized egg has frying,scrambling and boiling characteristics substantially the same as acorresponding unpasteurized egg.
 7. The egg of claim 6, wherein saidcharacteristics are maintained in the pasteurized egg for up to 75 daysstorage at 41° F.